Cable telephony



2 sheets-sheet 1 Feb. 9, 1932., R. c. MATHES ET Al.

CABLE TELEPHONY Filed Dec. 9, 1929 Feb. 9, 1932.

R. c. MATHES ET AL CABLE TELEPHONY Filed Dec. 9, 1929 2 Sheets-Sheet 2Patented Feb.. 9, 1932 stares l,844,tZZ

PATENT QFFICE ROBERT C. ErIAHES, OF lJtYMNG, AND ARTHUR W. HORTON, JR.,F EAST ORANGE,

TO BELL TELEPHONE LABGRATOl-IES,-INCORPORATED, GF

'Njt YRK, Y., A CORPORATION OF NEW YORK C LBLE' TELEPHONY Applicationfiled Ecceinber 9, 1929,Se1a1 No. 412,612, and in Great Britain ,August29, 1929.

'lhis application is a con lnuation in part ci our former applicationvtierial No. tlfl,

illed lune lln lQQSl for cable telephony.

The preent invention, While in many respects of general application.relates specifically to the problem of speech 'transmission over a long,deep-sea cable .such as a sub marine cable across the Atlantic Ocean-`The intention will be described with particular reference 'to thisproblem, although it will be erident as the description proceeds thatthe intention iu many oil its broad features as well as iu ce ainspecific aspects isapplicable to other types of transmission and is not,therefore, limited `to the transmission of .speech nor `to sulinnarinecable transmission. For eltample, high attenuation, the existence ofnoise d ortions, long time constant, ctc., are diilicul commonlyencountered to varjjfing ct'teits in radio transmission and in land lirl, nis, :is Well as in deep-sea cable transmit-'suon; so that theinvention, while adapted to a specific type ot transmission r tern, isnot to be construed as limited in tllereto.

lllhile the types ot actual cable systemsl to rvlliclr the invention isa; ,ilicable may vary widely among the iselres, a cahle Which will serreas an illu ,i ativo example is one consisting ot a single spancontinuously loaded, pretend"l with a nichel-iron alloy et special compion, boat treatment and manner of app ication as dif-sclosed, 'forexample, in United iltates patents to W Elmen 1515.543., of ,-luue el,192) and O. E. Buckley ot June 1, 1926; Suche cable may he assumed, torpurposes ot illustration, to have a total attenuation ot the order of100 db. und a time et transmission ot one-quarter so con d.

rllo be usr-etal `tor telephone communication, such :i rubio nur-:t headapted `for connection with land telt-phone sys ems, which may, for ciunple, coter continents. ln .tact the entire .illriiur circuit betweentwo talking parties may be conceirerl ot' as corgiprising` as a centra!portion l cable with terminal repentir circuits, and as eKtr-msions ofthis, sito tuo hind lines, one at each end olf thc cable,

'lil

each oit which may be hundreds or perhaps thousands of miles in length.

In such a system, among the outstanding transmission difiicultics may hementioned: the excessively large attenuation to currents et allfrequencies; the distortion arising from the unequal attenuationproduced in the lines, particularly in thecable, and also that producedby the various pieces of apparatus and by the cable, including thehysteresis effects in the loading n'iaterial; the noise, Which may haveits origin in the cable or in the huid lines or inrcircuits to which thecable and lines are exposed, and also in the individual piecesotapparatus; and various eliecsot a transient nature, principal ot whichare reflection,` echoes, switchinP noises, earth currents, the differenttimes of transini on of different frequencies, and the charging ordischarging effects of the cable. Another diiiiculty, somewhatdili'erent in character from those mentioned above, is the timerequiredto transmit from one talking party to the other.

Certain of these difficulties are functions ot the circuits themselves,for example, certain kinds ot noise, echoes, and the like, which yieldfor their solutionin part as least to a proper circuit design. Others ofthe diliiculties are ot a more complicated nature and are functions ofamplitude or frequency of the transmitted currents, ory of time. Amongthese latter are the distortion due to unequal attenuation, that due tomagnetic ctl'ects in loading and that caused by certain circuittransients.

Moreover, the ditliculty of the problem is increased by the tact that anattempt to reduce trouble ot one kind sometimes increases trouble oianother kind. For example, the energy level to which the currents areadjusted et 1an-ions points in the system cannot be deto mined fromattenuation alone, but must be consistent with noise level and thedistortion that a function ott energy level either in apparatus orcircuits. For this reason especially, the multiplication of apparatusshould he avoided where possible.

Certain of the factors which influence transmission remain substantiallyfixed so long as the circuit is not changed. For example, thetransmission time tor any given through-circuit will be substantiallythe same vthroughout the connection. The distortion produced in thesystem bythe message currents, and that due to circuit constants willobviously be substantially the same "for given adjustments throughout.exposure will, however, vary widely. A

practical system to give reliable transmission with a practical degreeof rinderstandability,

of the speech as received, notwithstanding the distortion within thesystem and the noise to which it is subject.

A related object is to eiect this transmission in a two-way systemoperative one way at a time with provision for avoiding mutual loch-outand harmful eimiects of echoes and regeneration around a sending andreceiving loop.V

To eiiect two-way transmission, a switching system 'for each transmitterand receiver, Linder voice control', is preferably used, oi' theso-called fcourier type. Such a switching system per se is disclosed inUnited States patents of R. C. Mathes 1,829,805 and 1,829,- 806,November 3, 1931.`

n Features oi the present invention comprise: suitabledistortion-correcting, noiseprotecting, volume regulating, andtime-controlled circuits together with amplifying and switching meansall to be described more in detail hereinafter. 4

Where the foregoing general description including the objects andfeatures mentioned,

refer to speech transmission, and while the following detaileddescription mentions speech throughout, applicants wish it to beunderstood that the invention comprehends transmission of wavecomponents occupyingV a frequency band whether these waves representspeech or something else. y Also the frequency band need not, oi course,be continuous but may consist of superposed narrow bands, as in the caseof multiplex carrier wave transmission. 1 Y

For a detailed description of the invention reference will be made tothe attached drawne's Fig. 1 is a schematic diagram of a terminalcircuit for the' cable for connecting the ,cable to a land line; andFigs. 2 to 5 inclusive, show curves which will bereerred to indescribing the operation of the system.

ln Fig. 1 the land line LL is connected to the cable CL by a four-'wirecircuit comprising the transmitting circuit TC for Vrepeat ing wavesreceived from the land line into the rllhe noise due to` cable and areceiving circuit RC for repeating waves received from the cable intothe land line. Y

Before proceeding with a description of the circuit of Fig. 1, referencewill first be made to Fig. 5 which shows the levels to be maintained atdiiierent points in the system,

these levels being given as illustrative and not as limiting. The levelsin Fig. 5 are given with referencev to an arbitrary Zero level shown bythe line 0 0 which may for conveniencebe taken as standard level forspeech waves at a subscribers station for normal telephonie transmissionand reception. 'The conditions at the incoming'end of the land i line`shown in Fig. 1, are indicated at the leit in Fig. 5. The dotted line aindicates the level of speech received at the station in Fig. 1 from theland line, this level being indicated as 30 dbfbelow zero level,although in practice this level may be anything between zero and a lowvalue such as -30 db. If we assume a total mean effective cableattenuation of 100 db. speech atzero level at the transmitting end willbe at a mean effective level -100 db. at the receiving end as indicatedby the line Zi. The power of the noise picked-up in a cable and measuredat the receiving end is assumed to have a mean effective level of about90 db. Itis assumed that an effective margin of 40 db. between speechand noise will give satisfactory articulation. In order to maintain thismargin between speech and noise at the receiving end, it is necessarythat the speech power at the transmitting end should be db. which asindicated bythe line c oi Figp will result in received speech at thelevel 50 db. giving a margin of l0 db. above noise. This means that thesending amplifier gain should be db. and the receiving amplifier 'ga-iiito bring the received speech to zero level must be 50 db. The totalampliiier gain in the transmitting and receiving circuits of Fig. 1 musttherefore be 130 db. Such a high gain would result in singingaround theloop formed by the circuits TC and RC of Fig. 1, if this loop wereclosed, since it would be impossible to maintain at all times a linebalance for the cable CL and for the line LL capable of introducing aloss of the order of db.

For the above-noted reasons, suitable-cin cuit establishing anddisabling means, reieri-edv to for convenience as switches, are providedin the circuits TCand RC for connecting these circuits one at a timebetween the line LL and the cable CL. Similar switching circuits are, ofcourse, provided at other stations to which the cable may be connected.

T he switching devices jor alternately disabling the circuits TC and RCfor enabling two-way repeating between the line LL and cable CL might becontrolled directly by flo Honk with the invention 'to employ elia-eealewiteh .roiniollinej We. ti'aneniitted over the cable oi eonti'elliingsu'itehe` .ewitehee t i (lii url'ents tlewfeising; the System. lepi'el'eiahle in accordance et a dietant station, it the oi'iginatingstation being' 'eetly hy t le -voice oui-rente. -oem'intion in generaltenne `will tiret he en of the terminal eiieuite of Fig. l, itaeeiunez'l that the eahle terminates at nuit Station in a eii'enit Whiehis the @nai-t of that ehou'n in F 1, and the oi ih will he clear i'oin aden olf lliggj. l. i. ovei Ytoi' the inonient, the epenaetui'e et theepeed-ainplitying, Wavepine.. volume'entioh ete. devices, the epitechineoniingi` li'oni the land line LL is y 'irl at l() and passed tlueugghhand .e lltei ll which contines the ti'ansinitted ilieei lll. delaydevice ll. and powei er lit to the eahle eneu'lt @L ly open. no thatrelay 17 moet he enel*- lieloi'e the epeeeh Waves ean actually into thecable. This le eeeoinplishel'l unueisenti-ol eli the epeeeh Wayee. eportion of iwhich i'e (livei'l'ed lieni the. eiieuit Til at l thiougi'hnoiel pi'eteetion oi f uf-le the i'eleafse otielevQO, This mitioeelreuit 19 may he of thev wie :i :igmlieiitioin Sei l HG Yinrondine' tothe Velay 253 et the f ement ,eh Wav opens; the wY-ieleaees ielay 21,this .ein hatteiv upg'vei' an A eontavt oit relay 2O to f :2l loee not.,hoiveven. unme- `.e hut allows: a ennuie lo l e fui-tu :uomentai'ilythrough its front eon `,i-wei'lnuznii of relay 20, this eileui't 'i-:lu-oueh windiuo oit relay and hatteiy lli-"f: 2?? le enel. 'ir/led forf-zueh ti hol/le itey axefniatu etti' ln'olien hy the ieleese el. T ne ii linny o any fleeueil 1'aine n' oneinth (5j i n ioeiilt et thief aeljubeln, 8. a Circ-nit it: elo y ai'nialu'li'ee 'el if w51 'vo ot razhmttu" Alle Velu l a ey, say 200 eyelee pei second and the length oftlieinipulse that ie sent maybe a smell Lti'eetion of a second. Thepurpose el this impulse is to effect at the distant terminal aswitching' opeiation to give the subscriber at .line LL Control of theComplete system and to pieyent Operation oi" the evitehee at the distant'tei'i'ninal oye;` the land line Connected te that terminal.

Relay 2O when it Wan released by the inltial Spee :h Wai/'ee also closdCircuit at ite` lowei' armature and haelt Contact thi'ough ha tei'y 30,high resistance 31, and eoildensei 32., causing` thie eondense' tocharge slowly throiilgh the resistance 31. (1n the attracted positionoit` relay 20, eondeneei 32 was discharged thi'oueh the eiieut includingthe aiinatul'e end fi'ent Contact of the relay ieeietanee Altet' esuitable time interval which may he Controlled hy dimeneioning theeapaeity et condenser 32 and the resistance of element 31? condenser isfully eliai'ejed and current from battery Howe through i'eeietanve 34eand relay 35 .in sullieient amount to cause the eviei'gization of relayRelay 35 in operating Closes: a eireuit freni battery 3G? uppei:nnietuie a nd beek Contaet ot relay 37, .inner lippe" armature and iontContact of izlay u8 (normally opei'ated), eontaet of ie .lay 35.,Winding el relay 17 sind Wii'ldings oi relays Al0 and 40', eaueingi theopeietion ot `relays 17 and 4() and 410". Relay 17 in opel-ata closesthe eireuit TC Se that epeeeh Wayee oil-cuit RC eo that none of thetransmitting eneigggy is allowed lo pase into the receiving Circuit.Relay jl-.O opens the eoiiziiei receiving; eiieuit so that it ieunaieeted by any Courier current that might arrive at the station attenit has been Seized ae a t 'ansinitting Station.

The speech ie delayed in the delay deviee 141 a eullieient time topermit ielriy 17 (and relay 40) to he fully operated before the Speechaii'ivee atthe Contacte ol Velay 17 so that none olf the Spee/eh lost hythe action et elinping. Relay fl-O in operating closes a circuit throughite loWei-nieet aifinatiii'e .find trent Contact, 'relay l1 and hatteiyCausing' the operation oit' ie.,ay Ll1 which (losen a Shorteiieuitaeiese the eii'euit RC, the pui-poile ol' Which will be described later.

Relay 2O remains ieleaeed long; as speech Wax/'ee ai'e being receivedtroni `the land line 1111 thm-it ie, as long); as the suheei'ibeicontinues: talkine9 so that i'elaye 35, 17 ans'l 410 and 4.0 i'eineinoperated throughout this period. These Telegate zleo remain eiiieiatedtoi' such additional time as ie required for the Speech which Stored inthe delay device 14 to have paeeed into the cable eiieuit. The time elthe speech delay in device 14twill he deseiibed late on. i

The operation at the distant terminal will be clearfrom considering theoperationof the circuit'of Fig. 1 in respons-e toY Waves received fromthe cablev CL. Speech initiated at theV distant terminal sends out fromthat terminal an impulse of courier current from a generator similar to2 5, but having a different frequency, for example, 250 cycles vpersecond. The control circuits for e'ecting the transmission or" this wavefor a momentary interval may be identical to those vdescribed above inconnection with this figure. This courier Wave sent out from the distantterminal over the cable CL passes through the filter 29, is received andamplified at 42, and passes through filter 43 into amplifierrectifiercircuit 44, Where it is rendere-d suitable vfor operating relay 37.`Relay 37 in operating opens at 4its upper armature and back Contact,the circuit that is adapted to be closed by relay 35, extending frombattery 36 through normally closed Jfront contact and upper armature ofrelay 38, for operating'relays 17 and 40 and 40 under control of relay35. rThis circuit being opened, prevents the energization orn relays 17and 40 and 40, if the subsc 1iloer on the land line LL should starttalking after control o the connection has been initiated by speech fromthe subscriber at the far terminal. Relay 37 at its inner-lower armatureand jfront contact closes a circuit from battery 46, conductor 47, andWinding of relay 16 causing this relay tooperate and open the circuit TCat a point between the elements 11 and 12. 'This insuresthat noisereceived from the cable or otherwise incident upon the receiving circuitwhich might findits Way across the hybrid balance circuit 48 shall notaffect the relay 2O and cause false operation of the terminal switchingapparatus.

Relay 37 at its loivermost armature and front contact closes a circuittrom battery 46, conductor 49, and right-hand Winding of relay 50,causing this relay to operate and conneet receiving circuitRC throughspeech pass tilt-er 51 and noise-protection circuit 52 to relay 38. rlhereceiving circuit is now in condition to receive 'speech from thedistant cable terminal since relays 4() and41 are both deenergized andrelay 50 is energized preparing a circuit for the speechA to control theoperation of relay 38. Relays 37 and 50 are made sloW-to-release toinsure that they will remain operated until the speech which initiatedthe sendingcut of the courier Wave from the distant terminal has arrivedat the receiving station.

Speech arriving from the cable passes amplifier 53, speech pass filter54, corrective eXpander 55, attenuation equalizer 61, volume expander5G, compensating control 57, delay device 58, receiving end equalizer59, receiving amplifier GOand into the land line LL 'where it istransmitted to the distant land line subscriber.

A' portion of the speech currents are diverted into the circuitextending through armatures and front contacts of 4relay 50, filter 51,noise-protection circuit 52 and these cause the operation of relay 38,(elements 52 and38 being identical With elements 19 and 20 describedheretofore.) Relay 38 in releasing closes a holding circuit for relay50'eX- tending through battery 61, upper armature and back contact ofrelay 38, outer left armature and front contact of relay`50, andlefthand Winding of this relay, so that relay 50 is held energized aslong as speech continues to be received, notwithstanding the release ofrelay 37 which takes place at about the time tle initial speechisreceived or slightly therea ter.

Relay 38 at its lower armature and back contact closes a substitutecircuit from battery 46 through conductor 47, for holding relay 16operated after relay 37 releases. Relay 38 at its inner upper armatureand front contact opens the circuit controlled by the front contact ofrelay 35 so Vthat this circuit remains opened afterrelay 37 releases.

When the talker at the distant cable terminal ceases talking. relays 50and 38 remain operated for asufiicient time to permit the speech storedin delay device 58 to pass into the line LL and then these relaysrelease, the

cessation of speech releasing relay 38 and this in turn releasing relay50.

The timing and the sequence of the operations above described are madesuch that complete .control of the connection is obtained and maintainedby thesubscriber Who first i starts to talk, as is described also in thepatents of" R. C. Mathes referred to above, Nos. 1,829,805 and1,829,806. While various timings and different sequences of operationsare feasible, the preferred timing and sequence Will now Vbe indicated.Whichever talker initiates talking first Will cause the arrival at thedistant station of courier` current betore the courier from that stationarrives at the station Where the speech is first initiated. rlhe arrivalof such courier immediately encrgizes relay 37 which prevents thetransmitting circuit from being made operative under control of relay35, that is, the station at which the courier first arrives ismaintained as a receiving station and is prevented from becoming atransmitting station. a transmission time T for the cable, it ispreerred to delav transmission of the speech for an interval T after thecourier is sent out. One advantage of this is that if both talkers starttalking at nearly the same instant, the courier first to arrive at thedistant station meets a condition of silence, for it arrives during theinterval in which the speech at that station is being delayed. If thereWere no time interval betvveenthe sending out of the courier and thespeech, in those cases Where both talkers start talking very nearlyAssumingV elli elli

tra

z cient simultaneously the courier lirst to arrive at the distantstation would ineet the condition that the transmitting amplifier 15 atthe latter station is sendingr into the cable speech oiierig;Y at hi hlevel. and this condition would render niore fflnncult to select thecourier and ii cutting-olf ol" the transmitter at that station. lt ispreferred there re to delay transmission ot the speech by an inter ralal er the sendingl out ot the courier. This is accomplished by delayingthe operation olf relay until time T, after the sendingij out ot thecourier, in order that power ainplitier shall .rcinain disconnected:troni the cable `For that interval. The delay produced by de 'ice lflis inade slightly greater than iniernl T to insine '.liull operation ofrelai' heliorc the speech reaches the break point in the circuit, sothat clipping77 is aroided. 'l`he delay produced by device 14 nia)r beof the order ot .0l or .02 seconds greatn er than the tinie interval l.llor a similar reason when the speech beine; received from the` landline ceases, suliicient hang-over inust be provided for relay te holdrelays 1l' and 0 o oei'atcd for an interval after cessation the L cach.`equal to the time delay intro duced at dcrice la or pret ably slightlygreater tiine to prevent terminal clipping ot with Weak endings. llerexample, this hangover nifty loe of the order oi" .l or .2 sends. lllhensaeech received 'from the le ceases. relays and 50 operate as described:litter a hang-over interval sulr'ito suppress echoes from the landline. relay lli being; thereby held operated 'until a liter such echoescease or have been ri-iduced to an innocuous level. This hang;- oifertime may he ot the order ol' a :teuf hundredths ol2 a second dependingupon the lei h o'l the connected land line.

the cessation `peet-.h received over the Urine which time receiving'circuit i held inoilniiratiif'e. this circuit l operative to receiveYtroni the an appropriate time interval. deif.' the tiininu ot relays 35and ell. i t this n"nt are that power innen send in; encre-y at high welinto the cable circuit. This circuit is ,siuldiinlj.Y d onnectei'l treinthe ca by re liaise et rc. if? and circuit RC almost siniultaneouconnected to the cable lov the felezu-ie ol relaiY -l-(l. lili theentire receivin?,v if: lll i-.verc :rendered op .ve at this uant.disturbances cue t eurrei'its in ie cable a tions tahingr "il Ws in thel s throun'li lne recoivinp; cir`r i into the land line und so on tosubscriber. 'llo prevent this, rey .ll and -ll are timed .so that relay4l is not released until a short interval. alter re lll-ase ol relay l0.A short-circuit is thus maintained by relay lll across the receivingcircuit for a short interval after the am lilier strongest, earthcurrents and echoes received A from the .lll

calile to be d'isipatod in the input e annui circuit oil bollorecont-act of ll-l opens. 'ifhe amplifie 53 contains su'lllclent lose todissipate these ground currents1 and prevent rlisturbinigi ellectsvtrono t ein. 'lhe release oit relay il can be delayed l'or about linie3T afer release of relay 40 the receiving circuit RC need not be in f'"'ou until the last ot the speech troni L ircuit if@ has reachedtheother terininal oft the cable and has there conditioned thetransinittingcircuit tor operation and until the courier troni thatstation has traversed the cable, followed T- tinie therealter by thespeech. hns a considerable tune swailabie in which to dissipate the L.dill'ercnt from that of normal speech and it is pointed out in thoseapplications that the s. ual-tonoise ratio may therefore be iinproved bydistorting` the speech so that its energy distribution brings thevarious separate components in the distorted speech Waves on the averageto higher energy levels than the corresponding` noise components. iluadditional advantage is that in many, if not inost, cases the distortedspeech is of such shape that the ditlerence between peak and averageenergy levels oi the speech is-reduced so th.;L the speech niay be sentat ahigher av` orage energy level without overloading` the tra emittingapparatus, particularly the ampl'ilier. The horizontal line L in Fig. 4rep` rescnts a condition Where the normal speech y/ has been convertedto a constant energy level over the essential 'frequency range,assun'ied as 300 to 3000 cycles per second. ils pointed out in theHartley and Alici applications this type ot distortion is advantageousin cnahli the speech to over-ride the noise for the r .ons brieflyindicated above. The line 7i may represent a higher transmission levelthan the curve g but no greater load on the iransinittingl apparatus asregards producina` overload distortion in the apparatus as is disclosedin those applications.

'lhe filter 0 passes the range 300 to 3000 cycles: per second butsuppresses both lower and higlher frequency components. One reason torthis is that distortion due to 1nodulario l". It I) tion in the cableloading is reduced as is disclosed in co-pending application of Buckleyand Hartley Serial No. 341,623 filed February 21, 1929, (Patent1,809,828, J une 16, 1931.) A reason for suppressing the highfrequencies is that singing around the terminal circuit TC-RC mightoccur at these high frequencies if they were not suppressed.

rlhe attenuation of the cable for the higher frequencies is much greaterthan for the lower frequencies so that it is advantageous to amplify thehigh frequencies in the speech band more than the lovv frequenciesbefore impressing the Waves on the cable or after receiving themr fromthe cable or at beth the transmitter and the receiver. The distortion ofthe Waves to compensate for the unequal attenuationY is therefore suchas to amplify the higher'components to a greater and greaterv degree asthe frequency increases over the band, as indicated by the right-handvportion of curve 7c. y

Below 11000v cycles the curve 7c might be extended as shown by thedotted portion ic', if it Were not for the effect of cablenoise. Cablenoise in general maybe due to static tively small. The resistance noiseis distributed over the Whole frequency rangeand is substantially flat.Static as it exists in the atmosphere is likewise assume@ flat,

but the shielding effects of sea Water and cable sheath are morepronounced athiglier frequencies, so that actually the noise will appearat thel receiving terminal of the cable as distributed mostly over thelower freiquency portion of the transmission range of interest. Thecurve Z in Fig. 4 may be assumed to represent roughly the distributionof cable noise at the receiving end in an illustrative example. If thefrequencies in the lower speech range Were sent out at a volume levelindicated by the kcurve k', 'this would give-practically no margin overthe noise, indicated by Z. On this account it is preferably to raisethel amplitude of the lower frequency components somewhat as indicatedbythe full line curve 7c.'

' The actual shape of thefrequency amplitude curve of the transmittedspeech Will, of course, vvary Widely in each specific instance and thecurves of 4V must be taken merely as illustrating the principles uponwhich to proceed in determining the amplituale-frequency distributionofthe outgoing Wave, and not -as in any sense limiting. Moreover, itmust be borne in mind that the curves of Fig. 4 show only the generalshapes of the curves as regards relative amplitudes of the differentfrequency components and do not pretend totalre account oflevelchangesdue to amplification nor to the effects of vol-V ume control orcompression, but only the shaping due' to the ,equalizer 11.

` Itis the purpose of the sending-end equaliz'er l11 to kproduce therequisite distortion in the transmitted Waves to compensate for thedistortion mentioned'above in the detailed description of Fig`.4.` Itmay and generally Vmayalso introduce a distortion of such character thatthis may, in part at least, be coinpensated for by the equalizers 11 and59.

The circuits of the equalizers may be of any suitable designV but arepreferably of the constant resistance network type as disclosed in thepatent to Zobel 1,603,305, dated Gctober 19, 1926, and as more fullydealt with in the article by Zobel published in the Bell SystemTechnical Journal for July, 1928 at pages f,438 to 534 inclusive. andresistance noise, the'latter being rela- V'JShevoluiiie control device12 and the compensating control device v5? may be of the type disclosedin'an application of Mitchell,

SerialfNo. 329,203, filed Dec. 29, Y1928, corresponding to BritishPatent 334,899, this being a type in which thevolume of the waves sentoutfrom the device is maintained substantially constant froni'instant toinstant for varying levels Yof input volume. This is accomplished, forexample, by providing a vacuum tube circuit in Which-the operatingpoint'on the tube characteristic is varied in accordance With the levelof the incoming Waves so as to varythe degree of amplification in thetube'iii such a Way as tomaintain the output level substantiallyconstant.

As indicatedin Fig. 1, the volume control 12 and the compensatingcontrol 57 are interrelated so that when the gain of element 12 isincreased, the gain of element 57 is correspondingly decreased to keepthe gain around the circuits TC and RC substantially constant. Themanner of vaccomplishing this inter-control ymay be as disclosed in theMitchell application referred to. It is not necessary so far as thepresent invention is concerned' to employ an automatic volume control at12 and 57 or to interconnect these, buttlie' volume-may be controlledmanually in both the circuit TC and the circuit RC.

The volume compressor 13 may be of the type Vdisclosed-in priorapplication of R. C. Mathes, SerialNo-15, 227, led March 13, 1925,(Patent 1,757,729,-May 6, 1930), or British Patent 255,221, and thevolume eX- pander 56 may be of the type disclosed in the same Mathespatent, or in the British patent. The association of the volume control-12 and the volume compressor 13 as dis- Lai/14,422

closed in F l ie also disclosed and claimed in prior application of R.C. hlzithes, Seriell lio. 350,971, filed Mei-eh 29, i925), (Putent1,816,599, Juli7 28, i931).

le accordance with u iieeture oit this iui'eutioi'l, the eu'ciut 18 'foroperating the exritchiiig devices der ired 'from the treuemi tingcircuit TC et e point io!lor:i:sig the Vvolume eoieLrol l2 zuidepeeilicelly et e point between volume control l2 :uid

'v d1une joui preeeor l? The Connection oi tl :it this; poli eA el.

ruoetly oi the reflui; Mil, 'one' `vowel @our ponente or the rel-et weekconsonant eoiuooueute. #dem quuheer ll lietorte the were; :le di toredi'zee lioth the Strong aud Weel; Speech components to u more nearlyeorietzmt energy 7revel, and the 'Volume control reduces the speech oi'stron tzillers and oli Weel: talkers; to ueetzuitiellj constant voluuu-ilevel. Couuee :u oi the `Voice control circuit i8 et the poiietindicated, therefore iueureet substantially een Stent operating'conditions; :for lhe 'reuih Connection of the noise protection eirei iti9 ellecti lr protects the voice control eircuite from ifelse operationby uoiec received over the lend line LL.

Returning to the coneideretiou of volume compressor 1B, the action oithie ezrei'liili ie diegramlueti elly l'iuilicuted in Fien 2A u"ereinput energy le ele are ludie 'i d by ehi. eud outer 1 energy levels; byordinates. Aeemilio@ lor eiemple that the ihoomiug Jnere'r hueiueteuteueous vz lueeI between the lier U und A, if the Volumecompref'fsor were oieittefh their the volume verintioue of the wirresimpressed ou the delay device .lil Vwould he the seine, e. h r the rangeUli? the elmreeterietie C heihg' drawn dcereee. providing echaracteristic l), hf'auiever, the 'volume renee of the diflerenteoiupoi'ieute iu the epeerh n ej; he reduced trom the renee Uli to somevelue lli the relative mhplitudee oi! the higher freq::erregtTcomponente in the weree ee they leere Volume eompreeiizor lieinsudcieut` en eruielize l l remy he provided to insure that highifrequeucy componente ure suliicieul- -uuiihueizexl iii the crible.'.lhie equalizer muy; he e iiielzrueted eimilerli`r to equalizer ll Lioliever 'the hi ,eher frequenoy eoiuponeure to .ie electr eel,

dated November 23, 1926, or may be any other suitable type oi dele);device.

The ampliiier l!" ie n Bower empliiier providing the requisite gein zuidpower capacity to meet the conditions already meeuseed earlier in thisappliintion.

Referring to the receiving cireuit RC, the

receiving ampliiier 53 may he of :my Suitable type haring the requisite:fg-ein.

The speech pees filter l ie e baud pese lilter capable of transmittingthe Wevee received from the :able end reprefientiug Speech, butexcludu'uigv the courier Waves. This lilter ee Well the other filterse111-- ployed iu the system may be deeigjgued in uecordance with thediecloeure of ll. 3. patent to Gr. A. Campbell, LQQMLM, dated Mey 22,1917.

The Volume exjpmuler 56 Huijy' he similar in Construction to tle volumecomitive# ir i3 but is adjusted to gifethe comerme ve ou. For exemple?referrug to 21, the exp-muh er is adjusted to ehzuigre from mi inputvolume rouge euch es @E to et erger out} )ut range euch zie OA.

For ease of decimi, it preferable 1 1 trol the charm eri tic of theentire between the compr e so that the lmtuer .may he the simple(fouverse opt the former in .its eetiou. Supp-oeiug that compressor lreduces volume hy u Square-root relation7 expander 5G may he mede toequere the input volumee and thus restore the volume relutioufi to theirorigiziele.A This shingle converse relationship een not exist howeverWhere there u um ,ferial emotuit of dietorlaioii between elements liland 5G, und it therefore et ggeous to reaching; the over-ell die :mderzpnuf l V e i i lz correct for the dietortiou he) iro expander 56 iuorder that the tortiou between the couiiufeeeor mesihle. For thie er muyhe are; Smell am gj purpoee :itteiuuition equal. er 6l end correctiveexijieuder 555 ere placed :iheed of Volume expander 56.

The etteountiou equalizer may he designed in accordance with the Zohelpatent eind ticle above referred to, or in any other suitable meneer, tocorrect for the relatively large attenuation suffered hy the high :firequenoy components iu trzwereio the eyeteul. That is, it dieorimiiuitesagainst the low *fre* queucy componer, :s el vd iii fever oi the hipjhii'rquenoy compone; ol. the trzmemitted Wevee ih Complementary nimeer tothe Sie# tem. Vhere :in equalizer lll used et the seudiugeud nedefierilied above, the equalizer (il should he designed to eoiupeiieete'For the distortiorL introduced by ietwork lll. es Well ae for the otherdistortione in the System, referred to.

The corrective expander 55 ie pf rticulurly needed Where the cable ie ofsuch character as to introduce u volume eoiupreeeiou etieet which isnon-linear. For exemple, referring to Fig. 3 in which inputinstantaneous volume is plotted as abscissae against instantaneousoutput volume as ordinates, the curve OF may represent the volumecompressor action of a cable loaded with a magnetic ma# terial. Thehysteresis of the loading material reduces high volume components morethan low volume components and produces a non-.linear effect somewhat asindicated by the curve OF. The corrective expander 55 may be similar inconstruction to the volume expander 56 already described, but isadjusted to have a non-linear input-output relationl over at least aportion of the volume range such as GH so as edectively to malte theover-all input-output volume relations for cable and expander of theform shown by the straight line Ol. Instead of providing a lcorrectiveexpander 55 and volume expander 56 as separate elements, these may becombined in one circuit to possessa characteristicy such as to give anover-all charac-V teristic for the cable and. expander asinoicated bythe curve OJ so that the volume is expanded in one operation to cor ectboth for the sending-end compressor 13 and the compression produced inthe cable. Y Y,

The corrective expander 55 is shown provided with an equalizer 65 thepuraose of which will now be described. rl`he cable acts to 'compressvolume not only as a function of the volume level but also as a functionof frequency. llhe higher frequency components undergo a greater volumecompression in the cable than do the lower frequency components. lt isadvantageous, therefore, to place an auxiliary control on the volumeexpander 55 to malte the corrective expansion of the volume a functionof frequency in such'manner as to compensate fully for the cablecompression. Referring to 3, the dotted curves between lines OF and Olrepresent the volume compression at diiferent frequency levels f1, f2and f3 of which f3 is the highest.

This equalizer 65 may be designed similarly in general to equalizer' 61,that is, it emphasizes the higher frequency components of he transmittedwaves and causes the corrective expander to raise to an input-outputrelation OI all volume levels, at all frequencies in the transmittedrange. To do this`v a volume level in the range Gilat high frequency f3must be raised more than the" same volume level at some lower frequency.such as f2, etc. Referring to Fig. 1 of R. C.

Mathes application, Serial No. 15,227, filed March 13, 1925, (Patent1,757,729, May '6, 1930), the auxiliary control 65 may taire the form ofan attenuation equalizer inserted in series in the control circuitbetafeen filter 12 and the rectifier 13 of that figure, so that therectilied current resulting from the higher frequency components of th-espeech waves is intensified relative to that resulting from the lowerfrequencies.

. are distorted to maire the higher frequencies have a relatively highamplitude, and this statement also applies to the waves leaving thevolume compressor 13. After traversing the cable, the high frequencycomponents are reduced in amplitude much more'than the low, butattenuation equalizer 61, and also the corrective volume expander 55with its auxiliarycontrol 65, bring the relative amplitudes and volumesof the high. and low frequency components of the waves to the samerelations (as nea-r as they may be) as they had at the output of element13 at the sending station. The waves entering the volume expander 56,therefore, are over corrected in that the high frequency components .arestronger relative to the low frequency components, than is the caseinthe original speech waves, since the waves are of the form resultingfrom the distorting action of equalizer 11.

Equalizer 59 inust therefore be provided to restore the frequencyamplitude relations to those of speech. This equalizer is thereforedesigned to introduce a distortion comple` mentary to that ofsending-end equalizer 11, and it may be'designed in the manner and be ofthe same type as that described above for the design and construction ofequalizer 11.

Equalizer ,59 in reversing the process of distortion performed bysending-end equalizer 11 restores the Waves to' recognizable speech andlassists in producing a favorable signal-to-noise ratio since itattenuatesnoise and speech components at the various fre-k quencies suchas to reduce the masking effects of noise and render the speech moreunderstandable, in the manner pointed out in general in the Hartley andAffel patents already referred to.

rlhe delay device 58 may be identical with the device 14 or any othersuitable type. The receiving amplifier 60 provides additional gainfor'the waves prior to their transmission on the land line.

The noise protection circuits 19 and 52 operate on a frequencydiscriminating basis to respond to waves having the characteristics ofspeech, but tobe unoperated by noise. The margin'of speech over noise asregards the protection of the'voice operated circuits is greater beforethe waves pass through the volui ie compressor 1.3 than afterward'sothat it is advantageous to connect the noise pro tection circuits aheadof the volume compresizo , circuits more certain.

and GS follow the equalizers 11 and 61 respectively., since theseequalizer-s emphasize components oi' high frequency, which are theweakest, and inale operation of the control as dl ln the :1y scloscd inl1" ig. l it will be observed ina the transmtting and receiving circuits.lC and it@ are directly connected to ne cable circuit Ch and do notemploy a lm l rid or diiierential balancing connection. This directconnection prcierablc, since a hybrid cruinection sends but halt theelfiergy into the cable. if a hybrid connection were used, therefore,the power output oli sendingond ampliiier l5 would need to be oi theorder e that necessary without a hybrid conl. the interest et preventingifalse on he switchinp,- circuits, however,

and to provide sh arp disc nnination between speech and couriercurrents, the hybrid balance 28 with cable balancing` network ll ispreferably employed for the courier terminal circuits. This hybridbalance together With 'the frequency discrnnination provided by n 'thelilters 2e and #i3 andthe use of different .ier lh'ecpiency Waves foreach terminal, d e a bi ,'h degree ci' discrimination beccn speech ornoise currents andthe courier currents.

'l-he lilter passes the couriern'aves but the sueech. lt also provides ahigh iinprrlsnce to speech Wares so that the cable is properlyterminated for both the courier and speech.

For simplicity oi' disclosure the circuits have been shown iu l asceilingl opened or clos d by relays 16, l?, Ll0, 40 and il and mecontrol circuits themselves by relays 23, 85, 3T, 38 and 5G. However,the on contenir/lates the use oi' any suitcircuit disabling; and cir iion oi a disabling; means in the Cil@ rt point ahead oit the volume l isadvantageous in that it prevents operation et the Volume control bynoise or by technet1 from the land line during;` the receiving; period.Such operation by noise 'would disturb the Volume control adjustment otboth the trnen itter and receiver since :a controls are tied together,and would 'tate a readjustment when speech again in the circuit TC.

lus/[rated in Fig. l, the sending-end :er 'fil precedes the Volumecontrol l2. h'le this order of connection ot these i two i i f 1.1 l' m1 meins in Lne circuit is in general to `oe of the speech componentsalike or to result in higher amplitude in the 10W frequency components.`When this is the case it is advantageous to have the volume control l2connected on the output side of sending-end equaliser ".fho operation ofthe volume control will then be determined in general by the magnitudeot the low frequency components. 'Vlhis desirable since the lon7trequency components in normal speech have energy. rlhis results in aproper rt on ci the volume control such as to `in incoiningsounds ot'different volrfine and 'troquet i distribution in propel' relation toeach other.

ln the cac, however, where the equalizer riesig" is such as to Inahe thehigher frequency components of the speech of higher amplitude, itadvantageous to have the volume control ahead ot the equalizer. It thereverse order were used, the operation of the volume control may bedetermined by the high frequency components of the speech Wares. Therelations between the high frequ ncy components of diilerent sounds ofnormal speech is different :from that of low frequency components `andhence the volume control may alter 'the Volume relations between sonnesin an undesired manner, it the eqiializcr precedes the Volume control.By placing' the 1volume control first, however, the operation of thevolume control is still dcterininefgl by the relatively large energy ofthe lou7 frequency components of the incoming; speech.

No attempt is made in Fig. l to show the actual location in space of thedilerent pieces ot apparatus. It is Within the invention to locate allof the apparat-us oi Fig. l at the saine Ifreoggraphical point or atditlerent geographical points as maybe most advantageous in anypractical cz se. For example, all the apparatus in Fig. l to the left ofrelay lo and compensentin@` control 57 including` the terminal oiE theline LL may be located ata geoo'ruphically distant point from the reineder ot the apparatus. Likewise, by eX- tending the control lead 47 thevolume control l2 and the conngcnsating,v control 57 may be located.,together with the apparatus shown to the left rt these two elements, atageoprapht cally distant point. The circuits TC and RC would then ineither case be extended as a fouiwwire line between the t-Wo distantlylocated points.

'llhe circuits TC and RC adjacent the terminal. of the land line LL areshown by dotted lines to indicato that the land line terminal includinghybrid coil 4S and balancing network ll may be located at ageographically distant point, even though all of the rest of theapparatus shown in Fig'. l is at the same or different Aegeographicallocations. This may mean` for example, that the apparatus shown in Fig.l is located at three geographically separated points. For example, theterminal of the two-wire line LL may be at Chicago. Theapparatus incircuit TC, including filter 9 and sending-end equalizer 11 togetherwith the apparatus in circuit RC, including equalizer 59 and delaynetwork 58, may be located at New York, while the remainder of theapparatus in Fig. 1 may be located at a distant point, such as atNewfoundland. As indicated hereinbefore there may also be located at NewYork (in the example given) the relay 16 and volume control 12 of thecircuit TC and the compensating control 57 or the circuit It will beunderstood that suita le amplifiers, corrective networks, echoSuppressors, etc. may be provided in the land line LL or in extensionsof the saine, as well as in the extended circuits TC and RC referred toabove. One advantage of extending the four- Y wire circuitsv TC and RCto a remo-te distance in the case of a long connection is that theoperating time may in some cases be reduced by reducing the number ofecho Suppressors that are required and thereby reducing the totalhang-overv time of the relays as well as reducing the liability ofmutual lockout.

Certain deviations from the system as schematicall indicated in Fig. 1have been mentioned allieve. `Cther alterations or modifica-- tions willreadily occur to those skilled ir. the art, in connection with adaptingthe invention to different transmission requirements. The invention isnot to be construed therefore as limited to the specific disclosure but`its scope is defined in the appended claims.

` What is claimed is:

1. In a system for transmitting waves oci cupying a band of frequenciesover a transtransmitting waves of a band of frequencies over a pathsubject to distortion, a network in the input circuit tothe path havingan amplitude-frequency characteristic such as to reduce all frequencycomponents of the outgoing signal wave to an amplitude level dieringfrom the same level for all frequencies by such amounts as to counteractthedistortion of the circuit, and means also in the input circuit to thepath operating under control of the impressed waves for reducing theoutgoing waves to substantially constant volume level.

3. In a signal systemvr for transmitting waves comprising a band offrequency components over a circuit which distorts the waves, means forpredistorting the signal waves in a manner to counteract the distortionproduced by the circuit, and means to reduce all outgoing signals tosubstantially the same volume level.

l. In a system for transmitting waves of a band of frequencies over apath which distorts the wave form, an equalizer circuit in theinputcircuit to said path for predistorting the waves in a manner tocompensate for the distortion in said path, and a volume controllcircuit between said equalizer and said path for reducing incomingsignals of different level to substantially constant level of wavesoutgoing to said path. y

5. The combination with a deepsea telephone cable of means in thetransmitting circuit to the cable for distorting outgoing speech vwavesto compensate the distortion produced bythe cable and for reducingoutgoing waves of varying volume to substantially constant volume level,and means in the receiving circuit of the cable for restoring receivedwaves to recognizable speech.

6. In a signaling system for transmitting Waves of a band of frequencycomponents over a path subject tof distortion, an input circuit for saidpath comprising the following elements leading to the lpath in the ordernamed; a wave-shaping circuit for compensating for the distortionproduced in the path; a volume control circuit for reducing incomingsignals of different amplitude level n to substantiallythe same levelfor transmission Vover the path; and a circuit 'control means forestablishing the input circuit to the path, said last means beingoperated under control of the transmitted waves.

7. A system according to claim 6, comprising a circuit derived from theinput circuit to the path at a point between said volume control andsaid circuit disabling means for diverting a portion of the transmittedwaves and utilizing them to operate said means.

8. A. system according to claim 6, including a transmission delayelement between the volume control and said means, and a circuit derivedfrom said input circuit at a point between the volume control and saidtransmitting delay element for diverting a portion of the transmitted.waves for operating said means..

9. In a system for transmitting waves of a band of vfrequencies,representing signals over a path having an appreciable transmissiontime, means under control of waves incoming to the system for sending acircuitcontrolling impulse over said path, a circuit controller alsocontrolled by said means for establishing an input circuit to said pathfor saidv signal Waves, and a delay device torv preventing theestablishment ot' said` input circuit to said path utter the sending otsaid switching impulse., for a` time substantially equal to tlietransniission time of said patli.

l0. t system according to claim 9 includ;- ing a delay device in theinput circuit- 'tor delaying the arrival ot the signal Waves at tliepoint of cstablislnnent: ott. said input circuit lor attimo slightlylonger, than tlie transmis sion time et said path.

ll An interconnecting circuit bet-Ween a noisy line and transmissionpatli tor receiv ing ivevcs representing speech or similar sie;nalsctrom said line and retransinitting Waves r sentino' sneecl?. oversaid transmis"- m patti, l t smis ion path producing distortion in thetransmitted "aves, said interconnecting circuit including a` waveshapingnetwork tor compensating :tor tbe distortion produced by saidtransmission patli, and a means tor effectively opening and closing saidinterconnecting circuit under control oit the Waves being transmitted, acontrol circuit tor said last mentioned means, and a noise }')rotectioncircuit in tlie input to said control circuit tor protecting` said meanstron] operation by noise on said line while permitting tbe operation oitsaid means under cont-rol ot said. Waves representing speccli.

l2. An interconnecting circuit Jfor repeating Waves received from a linesubject to noise into a transmission patli Wliicli distorts the Waves7comprising a Wave-shaping circuit connected to said line for alteringthe energy-'frequency relations of the Wave components to compensate forthe distortion produced in said petit, a volume control circuitconnected to the output of said network for reducing waves received fromsaid line to substantially Atlie same volume level, a delay de viceconnected to tbe output of said volume control for delaying transmissionolf the Waves -tor a short interval ot time, means for elllectivelyopening and closing said intercounectino' circuit at a point betweensaid delay device and said path, a circuit for diverting a portion ofthe Waves on tlie output side ot said volume control circuit and utilizing said waves to operate said means. and a noise protection circuit insaid 'diverting circuit for protecting said means from false operationby noise energy on said line.

A tivo-Way terminal circuit :tor a transmission path Wliicli is subjectto noise, comprising a transmitting an d a receiving branch, and meansunder cont-rol of botli transmitted und received Waves for effectivelyopening and closing at least one of said branches, means 'tor alsocontrolling said tiret means by tlm current other tlian said signalingWaves, and means ller protecting said firstmeans against operation bynoise energy.

14. In a transmitting circuit for a syste-1n including ai loadedtransmission lin-e,, meansV for shaping the Waves in saidl transmittingVcircuit tocompensate for distortion on said line, said means comprising:a circuit` torreducmg certainof the largeenergy low trequency componentsto a low: energy level to reduce modulation distortion 1n the line, a`

ponentsby the system, and a volume control to reduce input waves'tosubstantially con st ant. volume level.`

15.` A. system according to claim M14 includ.-

ing means to shape the Waves dependent uponl tlie noise characteristicof` the line whereby the Wave components are made to liavean.

amplitude margin over` noise. v

16. In a deep sea cable system for.4 transmitting Waves ot afbandoi-`frequency com` ponents, a sendingend equalizer for predistorting theoutgoing Waves to compensate for cable noise and distortioinaml a volumecon-V trclbetvveen said equalizer and the cable for reducing outgoingwaves oit ditlerent volume level to substantially the same volume level.

17. Asystem according to claim 16 including a circuit-establisliinglmeans between said volume control andA tlie cable,yand a. circuitconnected to tlie output side of said volume control for controllingsaid means by the transmitted Waves,

18. Inra deep sea cable system tor trans-` mitting Waves of a band oifrequency components, avolume controller reducing outgoing wavesotditterent volume level to sub" stantially the same volume level, and asending-end` equalizer between said volume control and the cable torpredistorting the outgoing Waves to compensate for cable noise andVdistortion.

19. The` combination with altransmission circuit which acts `as a volumecompressor on the transmitted Waves, of means for expanding the volumesof the transmitted Waves to compensate for sucli compression.

20. In a receiving circuit for a. loaded transmission line which acts asa volume compresser fortlie transmitted Waves, a volume expander forcompensating for such compression. l

21. In a transmission line ssytem in Whi cli the line acts as a volumecompressor on the transmitted Waves, means for compressing tlie volumebefore transmission over said line, and means at the receiving point forexpand ing the volumes of received waves to compensate for thecompression produced by botli` the line and said compressing means.`

22. The combination with a transmission line Wliich compresses thevolume ot trans7 mitted Waves unequally over the volume range, of avolume expander with an unequal expanding characteristic kover. the.volume Iline which compressesthe volume of transmitted Waves unequallyas affu'nction of frequency within vthe transmitted frequency range, ofa volume expander having an unequal volume expanding frequency charac-vteristic such as to compensate for the volume compression produced bysaid line.

24. In ya receiving circuit for a transmission line having unequalattenuation for ,Y

wave components of different frequency, an

equalizer for relatively emphasizing the coin- "ponentsthat are mosthighly attenuated by Said line, and a volume expander followingsaidattenuation equalizer, in said receiving. circuit.`

25. In a transmission system including a line having unequalVattenuation for wave components of diiferent frequencies, a wave Shaperand volume control ina transmitting circuit to said line, and:awaveshaper in a receiving circuit fromrsaid line, saidlast mentionedwave Shaper making Vup for the/unequal attenuation by said linerestoring thewave shape to approximate that at the output of the volumecontrolat a distant station on the line, a circuit-establishing meansconnected to said transmitting circuiton the' output side of` saidvolume control, another circuit-establishing means' connected to saidreceiving circuit on the output side of said vreceiving Shaper, saidcircuit-establishing means being operatedunder control of transmittedand received waves, respectively.

,26, In a receiving circuitfor a deep sea cable system, the followingelements in the order named, beginning nearest the cable: an

attenuation equalizer, a volume expander, a volume control, and aWave-restoring distorter. K y j 27. A circuit according to claim 26 inwhich a signal operated circuit lcontroller is conn nected to derivecontrol Waves'from the output circuit of said volume expander. y

28. In a deep Vsea telephone cable system employing a sending-end'waveshaper ina transmitting circuit to improve the energy frequencyrelations of speech waves for transmission over the cable, an equalizerin a receiving circuit for counteracting the unequal attenuation of saidWaves by the cable, a receiving'end Waveshaper in the receiving circuitfollowing said equalizer for performing the reverse alteration of thatperformed by the sending-end wave Shaper, and circuit controllersconnected to receive control energy respectively from the transmittingcircuitvat a point following said sending-end Wave shaper and from thereceiving circuit at a point between said equalizer and said receivingend Shaper. A

29. In a .receiving circuit for a submarine cable, said receivingcircuit adapted tobe made operative and inoperative alternately undercontrol of signals traversing the system, a plurality of disabling meansin'said receiving circuit at electrically separated points and meansoperating under control A cable, means for Vprotecting the receivingcircuit from earth currents from the cable comprising a plurality ofdisabling means renderingthe circuit non-operative at electricallyseparated points along said receiving path and in sequence'under controlof signals traversing the system with suflicient intervening time topermit disturbing energy to be dissipated.

3l. In a two-Way terminalcircuit fora deep sea telephone cable,transmitting and receiving paths, control circuits operated in responseto speech wavesin the transmitting pathfor disabling'said receiving pathat a point adjacent the cable and at a point remote from the cable, saidcontrol circuits operating, when rendering the yreceiving path opei'-ative, to establish the path first near the cable i and later remotefrom the cabley whereby earth currents are dissipated iii the receivingpath beforethe path as al Whole is made operative.

32. In a two-.way terminal circuit for a deep seatelephone cable, atransmitting and a receiving Speech path adapted to be con' nected ktothe cable and rendered operative alternately, circuits forsending to andreceiving from the cable lwaves other than speech waves, and a 'balancedhybrid 'connection for connecting said Sending and receiving circuits tothe cable in conjugate relation to each other. Y

33. In a two`wayterminall circuit for a deep sea telephone cable, kaspeech trans! mission path anda speech reception `path,

adapted to be alternately operativelyassociated with the cable, asending courierwave circuit and a receiving courier Wave circuityconnected, in Vconjugate relation to each other, to said cable, saidcourier waves occupying frequencies outside the range of speech currentstraversing the cable, and a filter in the courier wave connection to thecable for freely passing the courier waves but suppressing speechwaves,said filter having a high impedance termination at speech frequencies. fV

34; A system ,according to claim 11 in which said wave-shaping networkis located at a geographically distant point from the terminal ofthesaid transmission path and from said means,said control circuit and saidnoise protection circuit. v

lud

35. A system according to claim l2 in which seid Weveeliepi1ig circuitenel volume control circuit ere located at e geographically distantpoint :troni eeicl relay Clevice, weve flirerting circuit Incl noiseprotection circuit.

36. l telephone System comprising :L euhecriher station1 e two-Wirecircuit connected thereto? terniinatingl in a long 'tour-Wire circuitconnectingl geographically separated gioie eeifl touruvre circuitterminating at the enel remote 'from seid subscriber etetion in thetrenemitting and receiving` circuitsj reeneetiifely, oit the combinationee claimed in clfiinfi 5.

3l. A telephone system comprising a deep een.. telephone cable7 afour-Wire termination therefore e lone* tour-wire telephone lineconinfected to .mill four-Wire termination., and e eulaefcrihere lineadapted to loe connected to the 'lom-wire telephone line et ite remoteen.fl Said .tourrv.ire termination comprising eenrlii and receiifins;bronches eecli containing circuit control ineane operated uncler controlot eneech Waves traversing the eyetem i'or alternatively elliectively7connecting; the eenrlinc; :incl receiving' bronches to said celile. onflmeans in seid four-Wire circuit eeogrrenliicolly remote from said cableteri'uinirtion including; :i sending-enel equalizer lor clietortino'outgoing' Waves to compensate for distortion in eaicl czihle and areceiving' enfl equalizer for restoring: received distorted eneech Wavesto recognizable form for retrmunieeion over the receiving' side of saicltour-Wire line.

38. A System according: to claim 37 in which there is; also located inthe Sending eide ot Fieicl form-Wire line leerlingA to the cable, ut :Lgeographically remote point from the cnhle terminotion. e Volume controlcircuit 'tor reflucng impressed Speech Wayesofcliflerent "volume levelto substantially constant level tor treneinission to seid cableterminationu 39. A evetein according to claim 37 in which .mieltour-Wire line contains et e point Anfeoei'ruphicallV remote from seidcable termiuntion o voliune control circuit in the sicle oli the linelending: to the cable nucl a comoensnting control in the opposite sicleof the linen ML A system accor-eline: to claim 3'? in which the seidsenclinencl equalizer and the eaiifl receiving' enel equalizer arelocated et a Aooint lietireen the elibscriliere1 line incl the cehleterininetion and geographically remote troni each. v

ln Witness Whercoh we hereunto subscribe our nemee this 5th (ley ofDecemher, 1929.

ROBERT (l. MATFIES. ARTHUR W. BURTON, JR.

